Comparators from 0.1 µg to 6000 kg

A mass comparator or comparator balance is a balance with best possible resolution and...

1. What is the definition of a comparator?

A mass comparator or comparator balance is a balance with best possible resolution and repeatability allowing determining even the smallest difference is mass. While window-range mass comparators are purely used for mass calibration and mass determination, full-range mass comparators are versatile and can be used for weight determination but as well for general weighing applications where small samples meet large tare loads or the large and small amounts need to be combined in one weighing process. Contact your local METTLER TOLEDO representative to receive a GWP Recommendation identifying the models suiting your personal needs.

2. What makes mass calibration so different?

In a regular weighing process, the balanced is calibrated and the individual weighing are against zero g, therefore the process is called "absolute weighing". With weight calibration, which is a specific type of differential weighing, the reference point is not the calibrated comparator balance; it's the reference weight against which the test weight is compared to. Reference weight need to be at least one weight class higher than the test weight. Each of the reference weights is again calibrated against another weight of higher class resulting to a traceability to the national prototype and finally to the International Prototype of the kilogram at the BIPM in Paris, France.

3. What applications are comparators used for?

The primary applications where mass comparators are used for is mass calibration. For lower class weights, in particular M 1-3, F1 & 2 classes, manual mass comparators provide results of sufficient accuracy. For weights of E1 or E2 class it is recommended to use either robotic or automated mass comparators as the measurement uncertainty is significantly lower, this mainly due to the obsolescence of the operators influence. In national metrology institutes (NMI's), which strive continuously for measurements with smallest uncertainty, vacuum or constant pressure mass comparators are utilized as these allow performing measurements at constant conditions. Influences such as geographic altitude, air buoyancy or weather conditions can be eliminated. National metrology institutes and metrology research center apply mass comparators for scientific research to measure smallest changes in mass or force.

Besides the metrology application mass comparator are as well in use in other industries where the performance of a regular balance cannot meet the customer demand. For these applications the comparators are referred to as higher performance balances.

Some of these industrial applications are:

Formulation – if tolerance levels are low and the save weighing range of the balance does not fulfil the instrument demands

Differential weighing applications – if the difference in mass is very small and an ordinary balance cannot provide trustworthy results

Gas filling – Heavy gas bottles are filled with a small amount of precious reference gas

Scuffing – Gears are analyzed on abrasion after the engine was run for a specified time in the lubricant of investigation

Force measurements – Measurements where an applied force is compensated by the weighing cell

4. What is the difference between a mass comparator and a balance?

Mass Comparators are of identical design and principle as an electronic balance. What differentiates the balance to the comparator is the performance, in particular the readability and repeatability.

According to regulations, Mass Comparators in use for mass calibration do not need to be calibrated, as the reference weight is calibrated and ensures for traceability to the BIPM and the definition of the kilogram. To protect your investment and ensure continuous constant measurement performance, METTLER TOELDO recommends performing preventive maintenance on a routine base.

Where mass comparators are in use in applications different than weight calibration, it is crucial to apply existing quality standards on the XPR-C balances, identical to other analytical or precision balances.

Certain about your Uncertainties?

Established calibration laboratories may have various comparators, which are in use on a daily basis to calibrate customer weights. With increasing market requirements and the need to calibrate weights of higher classes, the risk of hidden uncertainties increases by using a system built up over years. By using our equipment qualification service CalibCap, you will receive an overall uncertainty analysis of your currently installed comparators compared with regulatory requirements, and an indication as to whether the achieved uncertainties comply with accuracy requirements. All calculations follow the OIML R111 uncertainty analysis recommendation and are based on the technical specifications of actual and former comparators.

White Paper Collection: Weight Calibration

As partner of choice, METTLER TOLEDO provides in addition to innovative solutions a broad understanding of market challanges. For weight calibration, typical challanges to overcome are, productivity, the uncertainty budget and it's calculations. To learn on how to address such, read the whitepaper on:

Laboratory Catalog

Our laboratory catalog gives a complete overview of all METTLER TOLEDO laboratory products and solutions. It presents our broad portfolio of innovative products, software solutions and our service offering. It gives an overview of where you can find valuable application and laboratory know-how in order to stay up to date.

Free Trial Evaluation Period

Learn in a 45-day free trial period how the software will improve productivity and simplify your day to day work.

Quality Assurance

Mass comparators and climate sensors are installed with a click and do not require IT expertise. Comparator testing functionalities generate performance data which improves the reliability of your uncertainty values. Built in quality assurance tools ensure continuous regulatory compliance through monitoring of comparator performance and laboratory climate.

Compliance Through Customizable Processes

MC Link weighing methods and uncertainty analysis are designed in compliance with international metrology guidelines such as OIML R111, NISTIR 6969, JJG 96-2006, GM-P8. Modular method design facilitates adaption of process and uncertainty calculations to meet local regulations and specific laboratory needs.

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